The neoplastic process in human beings has been and still is the subject of intensive study. In order to obtain a better understanding of the disease, human cancer tissue has been studied in an effort to discover the cause, treatment, prevention and/or diagnosis of cancer. Early diagnosis of cancer is very important since it increases the chances of effecting a complete remission of the disease.
In an effort to utilize known diagnostic tools to detect the presence of cancer tumors, attempts have been made to demonstrate tumor specific antigens to human carcinomas. These attempts have previously been unsuccessful with many types of carcinomas since it has not been possible to segregate normal tissue antigens from abnormal cancer antigens and demonstrate the specificity of the cancer antigens.
In the efforts to isolate abnormal cancer antigens and demonstrate their specificity, attempts have been made to cause the formation of tumor specific antibodies and demonstrate their presence in sera obtained from animals immunized with preparations of human cancer. If consistently reproducible, the demonstration of the presence of tumor-specific antibodies in animal antisera would lead to the use of a valuable diagnostic tool.
In order to fully utilize the existence of tumor-specific antibodies in animal antisera as a diagnostic tool, a test must be developed which will demonstrate the presence of the tumor antigen in the blood of the patient. Procedures which have been devised have not proven efficient or sensitive in the detection of and differentiation between carcinomas originating at different locations within the body, or metastatic conditions.
Among the possible sources of antigens associated with human carcinomas which have been most extensively studied by investigators are adenocarcinoma of the colon and digestive tract, meconium, carcinoma of the liver, ovarian cysts and carcinoma of the breast. Since adenocarcinoma of the colon is one of the most widespread cancers and usually requires a surgical procedure for definitive diagnosis, after some gross symptomatology has developed, it has been among the most extensively studied.
Efforts to extract a relatively pure antigen associated with carcinomas or adenocarcinomas have met with either no success or are impractical from a commercial point of view since a process has not been found to make it possible to completely segregate such an antigen from normal tissue antigens and non-antigenic materials.
The presence of antigens which are stated to be specific to adenocarcinomas of the colon and digestive system by means of immunological tolerance and absorption techniques have been demonstrated, Gold et al., J. Expt. Med. 121 439-462 (1965). However, the practical and commercially feasible isolation of the antigen itself as well as its association with carcinomas and adenocarcinomas had, until the present invention, not been achieved.
The tumor-specific antigens have been previously shown to be present only in patients who have adenocarcinoma which originate in digestive system epithelium derived from embryonic entodermal tissue, i.e., esophagus, stomach, duodenom, pancreas and rectum.
It has also previously been demonstrated that the tumor-specific antigens are also present in the digestive organs of fetuses between two and six months of gestation, Gold et al., J. Exptl. Med. 122 467-487 (1965). Thus, for convenience, the antigen has been designed as carcinoembryonic antigen (CEA).
Not only has it heretofore not been possible to isolate and characterize the CEA by practical rapid methods, but it has not been possible to demonstrate its presence in the blood of persons having adenocarcinoma with a diagnostic test suitable for large screening programs.